Integrated circuits are formed by patterning successive layers on a substrate such as a silicon wafer. Patterns are transferred to the substrate using lithography.
FIG. 1 illustrates an exemplary lithography process. Light 105 is incident on a mask 110. Mask 110 includes a chrome layer 112 and a quartz layer 114, where a pattern of the chrome layer 112 is configured to transfer the desired pattern to the surface of a substrate 120 by interacting with a photoresist layer 122 on the surface.
Light 106 incident on chrome layer 112 is substantially reflected and/or absorbed by chrome layer 112. Light 107 incident on quartz layer 114 is substantially transmitted to the surface of a substrate 120.
The transmitted light interacts with photoresist layer 122, and changes the properties of the photoresist. For example, the light may break bonds in the photoresist so that illuminated portions may later be removed, or form bonds in the photoresist so that illuminated portions will not be removed. Substrate 120 with photoresist layer 122 may then be processed further to “develop” the pattern on the surface.
A similar process is used to form mask 110. For example, a photoresist layer is formed on an unprocessed chrome layer, and lithography is used to pattern the chrome layer with the desired features.
Like reference symbols in the various drawings indicate like elements.